One example is Parallels Desktop, they constantly mail me to upgrade but there is no information what system version they run on. So I downloaded the installer

One example is Parallels Desktop, they constantly mail me to upgrade but there is no information what system version they run on. So I downloaded the installer and just launched it. The installer did delete my previous version without asking any question and I was just left with the option to buy the upgrade... I had to restore a backup to find back my working version. Not sure sure if there are as many extreme examples: an installer that deletes the previous version, remove a valid perpetual license, without asking!